Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

I have a 5 year old Toro Powerlite.  Bought it last week used.  The owner said that it wouldn't start.  Turns out that the recoil cord was hanging out so much, they couldn't get a good pull to turn the engine over.  Anyways, fixed the recoil and check the carburetor needle and seat.  The carburetor seems clean and the engine starts on second pull.

I pulled the spark plug to check found that it was black and wet.  I think the previous owner may have run this engine rich or because the spark plug was not tightened properly.  So I took out the muffler to take a look at the cylinder walls and the top of the piston.  Cylinder walls looks good, no scoring.  However, the top of the piston is all black.  Seems like  there's a layer of carbon.  What should it look like if everything is running properly?  What do you guys think the root cause of the black spark plug and piston?

I ran the engine longer today and it seems to be running right, no smoking at all after a few seconds.  Also tipped the engine backwards to try burn all unburned fuel out of the bottom of the crankcase.  I didn't have any snow to test the performance of the snowblower, but the engine does seems to run strong and the RPM sounds even, no surging or smoking.  Apart from the loud exhaust and vibration from this little engine, it sounds pretty healthy.

I think I'm going to keep this machine for a couple years, so I've been cleaning all the oil and crud on the snowblower.  Should I pull the cylinder head off and clean the piston?  I think I probably need a new head gasket if I'm going to open it up.  Is there any benefit of cleaning the piston?  Or any detrimental effects of not cleaning it?  Also, there are 5 or 6 head bolts, what's the tightening torque?  The engine is a Tecumseh TH98 (similar to HSK600)

If I were you, I wouldn't be taking the head off.  Chances are that it's got more soot on it than carbon.  If the exhaust ports looked clean, the cylinder/piston crown will likely be cleaner.   The problem with two cycle engines is that they'd don't particularly like low rpm operation and run better at moderate to high engine speeds.   I suggest you adjust the governor to jack up engine rpms and wait for some snow to put it to work.  After you have worked it hard for half an hour or longer, pull the plug and take a reading.  If it's a nice tan colour as in the picture of the  plug that I posted just leave it.  If it's still black, make sure that the choke isn't partially engage during operation and also ensure that your carb float is working properly. 

If the float is hollow, it may have a hole or crack in it and fuel has entered thus making it lose buoyancy allowing excessive fuel into the main jet.  I had that happen to me once and for the life of me, I couldn't figure it out until I pulled the float and paid very close attention to see if I could hear fluid inside the float which I had overlooked previously.  Vigorous shaking clued me in on the fact that the brass float had a tiny pin hole in it and enough fuel had entered  to cause carb problems.   Getting the fuel out can be tricky.  I drilled a tiny hole on the top of the float that allowed me to blow into it and force the fuel out through the pin hole.  I then patched both holes with some JB Weld.  Problem solved.   Engine has been running great ever since. 

Thanks for the tip, Borat.  I examined the exhaust port several days ago.  Besides the coating of fuel and oil, it wasn't caked on.  It was easy to wipe off.  Also, the muffler was in pretty good shape. It just bothered me to see the black piston crown.  I just have an affinity to have my equipment clean and in top operating condition. 

Looks like I'll just pick up an new spark plug and run it a couple of times and get a reading on the plug.  I did check the float and it's still good, no fuel inside to mess up its buoyancy.  I'll just pick up new needle and seat, gasket, and bowl.

I all of my years of owning and working on two cycle engines, I've yet to see one that had a serious carbon build up issue inside the combustion chamber and I've worked on some very old two strokes.   The description you've provided would lead me to believe that the engine had been operated without getting up to proper operating temperatures and possibly too much oil in the fuel.  Not bad things for someone buying a used machine.  Chances are the engine is barely broken in and will have a long healthy life ahead of it. 

I've bought older equipment that was virtually new because they had sat in storage sheds for numerous years with very little use on them.   Usually, the owner had trouble with it, couldn't fix it themselves and didn't want to pay to have it fixed.  So a piece of equipment ten to fifteen years old had less than five seasons of use on it.  These gems are usually easy to spot because they look good cosmetically.  Very little signs of wear and tear.   If the engine turns over nicely and has a good spark, usually a carb cleaning is all it takes to get it running.  

One of the few things I appreciate about this Powerlite it is so lightweight and simple.  The engine is tiny, has no valves.  Exhaust port is straight shot out to the muffler.  No headers, just straight to the baffles.  Years ago, I played around with port and polishing on a small OS nitro methane RC engine, hard to resist when I got a Dremel and a small engine in hand.  Also played around with different exhaust lengths and backpressures.  This Tecumseh engine brings back memories of those days, and the recent discussions on modifying 2 stroke engines just fuels my urge again.  :)

Two stroke engines are mechanical magic!  Easiest thing in the world to squeeze more power out of and still remain reliable.  They can take a fair amount of modification before reliability becomes an issue.  All the while, happily pumping out impressive power for their weight and displacement. 

borat wrote:
I got addicted to the 2 stroke last year after driving a mildly modified go cart with an Italian engine.  I can't remember the engine or the HP.  The acceleration, sound, smell, open wheel, and lateral g forces feels just so raw.  It was ridicuously fun and worked quite a sweat.